Make an FX reclaim step one whole track's chain: drop the resume cursor, yield only between tracks

src/shell/view/fx_reclaim.cpp

@@ -38,7 +38,8 @@ ParkClock                g_clock;
 
 // TrackFX_SetOffline is ASSUMED to pump the message loop, so a plugin load can re-enter
 // the timer and land back here mid-drain. Fail closed: a re-entered drain would walk the
-// same items the outer one is mutating and double-write from a stale resume cursor.
+// same queue the outer one holds a reference into, re-running the very item that outer
+// step is still writing.
 bool g_draining = false;
 struct DrainLatch {
     DrainLatch() { g_draining = true; }
@@ -99,9 +100,12 @@ struct ReclaimHost {
         if (TrackFX_GetOffline(tr, fxIndex) == offline) return false;      // already there
 
         // DAW-VERIFIED: the same ten TrackFX_SetOffline calls mint ten undo points
-        // unblocked and ZERO inside this pair. One block per write, not per tick: the
-        // write itself is what pumps, so the block cannot avoid spanning a pump — it can
-        // only span as little of one as possible.
+        // unblocked and ZERO inside this pair. One block per WRITE even though a step is
+        // now one whole track: the write itself is what pumps, so the block cannot avoid
+        // spanning a pump — it can only span as little of one as possible. Widening it to
+        // the track would multiply that exposure by the chain length while suppressing no
+        // extra undo point (the discard form mints none either way), and a user action
+        // landing inside a discarded block can lose its own Ctrl-Z.
         Undo_BeginBlock2(project);
         TrackFX_SetOffline(tr, fxIndex, offline);
         Undo_EndBlock2(project, "", 0);